Oracle 11gr1打开数据库的闪回flashback

1. 确认一个数据库是否打开了flashback，有两个简单的方法：
（1）直接查数据库
SQL> select name,log_mode,flashback_on from v$database;

NAME      LOG_MODE     FLASHBACK_ON
--------- ------------ ------------------
ORA11G     ARCHIVELOG   NO     --> flashback未打开

（2）查看后台进程
Oracle@bmp1a:~> ps -ef | grep rvw |grep -v grep
oracle    9288     1  0 10:45 ?        00:00:00 ora_rvwr_ora11g   --> flashback已经打开www.linuxidc.com

2. 如果数据库没有打开flashback，那么将flashback打开：
（1）确定flashback的存储路径
SQL> show parameter recovery

NAME                               TYPE        VALUE
-----------------------------     ----------- ------------------------------
db_recovery_file_dest         string
db_recovery_file_dest_size  big integer   0
recovery_parallelism           integer        0
修改db_recovery_file_dest：
SQL> alter system set db_recovery_file_dest = '/home/oracle/flashback' scope = both;
alter system set db_recovery_file_dest = '/home/oracle/flashback' scope = both
*
ERROR at line 1:
ORA-02097: parameter cannot be modified because specified value is invalid
ORA-19802: cannot use DB_RECOVERY_FILE_DEST without DB_RECOVERY_FILE_DEST_SIZE
上面的错误，是因为在设置db_recovery_file_dest之前，一定要先设置db_recovery_file_dest_size，于是：
SQL> alter system set db_recovery_file_dest_size = 20G scope =both;

System altered.

SQL> show parameter recovery

NAME                               TYPE           VALUE
-------------------------------  -----------     ------------------------------
db_recovery_file_dest         string
db_recovery_file_dest_size  big integer    20G
recovery_parallelism           integer          0
SQL> alter system set db_recovery_file_dest = '/home/oracle/flashback' scope = both;

System altered.

SQL> show parameter recovery

NAME                              TYPE          VALUE
------------------------------- -----------    ------------------------------
db_recovery_file_dest        string          /home/oracle/flashback
db_recovery_file_dest_size  big integer  20G
recovery_parallelism           integer        0

（2）打开flashback
SQL> alter database flashback on;
alter database flashback on
*
ERROR at line 1:
ORA-38759: Database must be mounted by only one instance and not open.
上面的错误，是因为在打开数据库的flashback必须要mount状态下方可以，于是：
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.

Total System Global Area 5344731136 bytes
Fixed Size      2169104 bytes
Variable Size   2130708208 bytes
Database Buffers  3204448256 bytes
Redo Buffers      7405568 bytes
Database mounted.
SQL> alter database flashback on;

Database altered.

SQL> alter database open;

Database altered.

SQL> select name,log_mode,flashback_on from v$database;

NAME      LOG_MODE      FLASHBACK_ON
---------   ------------------  ------------
ORA11G   ARCHIVELOG   YES